As one of usages of a wireless device in the relevant technical field, monitoring and operation of various facilities have been carried out wirelessly. Various facilities are monitored in reference to sensor information such as electric energy and temperature, and data information such as abnormality notification. The aforementioned information from those facilities is mostly obtained through cable data communication. However, it is likely that the facility to be monitored and the monitoring place are remotely located, requiring the wiring work therebetween. Wireless communication may facilitate monitoring and operation of the facility far away from the monitoring place without requiring the wiring work.
There may be various facility set-up environments dependent on site as well as amount of communication information required for monitoring the subject facility. For this, it is necessary to select both the frequency band and wireless format optimal for the wireless communication in accordance with the set-up place of the facility and the communication condition. Considering features of the wireless frequency, it is likely that the high frequency leads to high communication speed and short communication distance, and low frequency leads to low communication speed and long communication distance. The same frequency may have different features dependent on the communication mode (LAN, Bluetooth (registered trademark)), and standard. This may cause difficulty in the work to construct the optimal wireless network by selection from those described above adapted to an EM environment and a facility set-up environment.
If the facility is generally monitored and operated wirelessly, it is necessary to determine the wireless format to be employed, carry out the onsite radio wave investigation on the frequency in accordance with the wireless format, and then construct the network. If different wireless formats are employed together in the network, the wireless devices at wireless frequencies for use have to be separately prepared. Combining those devices makes the network complex, resulting in the tendency that deteriorates ease of introduction and operability after such introduction.
Patent literature 1 discloses the structure that efficiently carries out wireless communication between respective mobile terminals and the base station using a plurality of communication channels. The wireless LAN access point is provided with a plurality of wireless LAN modules for the purpose of allowing simultaneous use of some of a plurality of communication channels at different frequencies. The respective wireless LAN modules have different communication channels. The wireless LAN access point detects the number of connected mobile terminals corresponding to the respective communication channels so as to transmit the communication channel information indicating the number of connected mobile terminals of the respective communication channels to the mobile terminal. This allows the terminal to select the communication channel connected to a smaller number of the terminals, and ensures efficient wireless communication between the respective mobile terminals and the base station.